This invention relates to a process for manufacturing an iron-phosphorous (Fe-P) alloy, and more particularly to a process for manufacturing a high density iron-phosphorous sintered powdered metal (Fe-P) alloy having excellent soft magnetic characteristics.
Fe-P alloy with its high magnetic permeability is widely utilized as a head-yoke material for an iron magnetic core dot-printer including a magnetic switch. In general, these devices have a relatively complicated shape, so that conventional plastic molding cannot be used to manufacture them. Also, traditional machining processes for producing them are very costly.
Therefore, according to the conventional processes, a molten Fe-P alloy is poured into a ceramic die and the solidified product is removed from the cavity of the ceramic die after cooling. This process is known as precision casting. However, since this precision casting requires melting of the metal alloy, in some cases undesired precipitation takes place during the solidification process and variations in porosity will be encountered inside the cast products. Hence, it is extremely difficult to reliably produce products having uniform excellent soft magnetic characteristics.
Several attempts have been made to overcome these technical drawbacks by employing powdered metallurgy methods to the forming of Fe-P alloy products. Since the conventional method for forming powder metallurgy products uses press-forming, a complete and perfect composition is hardly ever achieved, even if a large pressure is applied during the forming processes, because cracks will be formed due to these high compressive forces during sintering of the green powder.
In other methods, since the Fe powder has a relatively large average particle size, it has been proposed to mix a fine particle powder of either P or Fe-P into the Fe powder. However, when the prepared pressed-green product is sintered, the final relative density can be increased only up to 92-93% at most. Moreover, because coarse Fe powder is used, the mixing of P powder with the Fe powder is insufficient, resulting in non-uniform distribution of P powder. It is generally believed that the soft magnetic properties of the alloy are further degraded by an increasing degree of porosity and the non-uniform distribution of P powder. Consequently, the products made through the above powder metallurgy are found to possess less desirable characteristics than those manufactured by a melting process.